This invention relates to the provision of a shallow recess communicating discharge pressure and temperatures back across the width of a thicker portion of a hybrid wrap in a scroll compressor to compensate for the uneven thermal expansion that can occur in hybrid scroll wraps.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member has a base with a generally spiral wrap extending from the base. A second scroll member has its own base and spiral wrap. The two wraps interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and as the relative orbital movement occurs, the wraps move reducing the size of the compression chambers, thus compressing an entrapped refrigerant.
Scroll compressors are becoming widely utilized due to their efficiency, and other beneficial characteristics. Also, a good deal of engineering development is occurring with scroll compressors. As one major advancement, the shape of the wraps has deviated from a spiral. Originally, the scroll wraps were formed generally along an involute of a circle. However, more recently, more complex shapes to the wraps have been developed. While the wraps are still xe2x80x9cgenerally spiral,xe2x80x9d they do deviate from an involute of a circle. Various combinations of curves, involutes, etc. are utilized to form a so-called xe2x80x9chybridxe2x80x9d wrap. In a hybrid wrap, the width of the wrap varies along its circumferential dimension. Generally, in a non-hybrid wrap, the width of the wrap is uniform.
While hybrid wraps provide a number of benefits, they also raise a few challenges. One challenge is shown in prior art FIGS. 1 and 2. As shown in FIG. 1, a scroll compressor 20 has an orbiting scroll member 22 with a base 24 and a hybrid wrap 26. The non-orbiting scroll 28 has its own base 32 and wrap 33. As shown, the wrap 33 has thinner portions 30 and thicker portions 34. The reasons for, and configuration of, the hybrid wrap are known in the art. However, a problem associated with the wraps having thicker and thinner portions is illustrated in FIGS. 1 and 2. As shown, there is a relatively low pressure and low temperature suction chamber 38 on one side of the thicker wrap portion 34, and a higher pressure and temperature chamber 40 on the other. The chambers on each side of the thinner portion 30 would also be at distinct pressures and distinct temperatures, however, as explained below, the problem that is to be solved by this invention would not be as pronounced at the thinner portion 30, simply because it is thinner.
As shown in FIG. 1 schematically, there may be thermal expansion such as shown in outline at 36 at the thicker portion 34 due to the temperature imbalance between chambers 38 and 40.
As can be seen in FIG. 2, the higher pressure and higher temperature on the inner side of the thicker portion 34 causes a heat gradient across the width of the thicker portion 34. The same would be generally true at the thinner portions, however, since the thinner portions are in fact thinner, it is more likely that the temperature gradient will be not as pronounced, and heat would transfer freely across the width of the wrap. At the thicker portion, there is greater heat resistance, and thus a greater likelihood that the heat would not transfer across the entirety of the width 34, but would instead result in localized thermal expansion. This is the thermal expansion shown schematically and in dotted line at 36 in FIG. 1. When this type of expansion occurs, undesirable effects such as surface wear or galling between the end of the thicker portion 34 and the opposed base 24 of the orbiting scroll 22 can occur. This is, of course, undesirable.
In the disclosed embodiment of this invention, a recess is formed into the face of the thicker portion of the wrap such that localized thermal expansion is partially compensated, but not to the extreme edge such that this refrigerant in the recess is still separated from the suction chamber. In addition, discharge temperature and pressure refrigerant is communicated along the width of the thicker portion. Thus, the recess communicates the higher pressure and temperature refrigerant along the width of the thicker portion such that the heat gradient is only over a thin portion of the wrap, thus reducing the thermal expansion imbalance.
In a preferred embodiment, this recess is very shallow, and on the order of 0.0005 inch. Moreover, the recess extends between two circumferential edges, and to an inner edge. The recess preferably communicates with the discharge pressure chamber along the entirety of its circumferential width, to maximize the resistance to a heat transfer gradient.
These and other features of the present invention may be best understood from the following specification and drawings, the following of which is a brief description.